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Large-area microwire MoSi single-photon detectors at 1550 nm wavelength

We demonstrate saturated internal detection efficiency at 1550 nm wavelengths for meander-shaped superconducting nanowire single-photon detectors made of 3 nm thick MoSi films with widths of 1 and 3 $μm$, and active areas up to 400 by 400 $μm^2$. Despite hairpin turns and a large number of squares (up to $10^4$) in the device, the dark count rate was measured to be ~10$^3$ cps at 99% of the switching current. This value is about two orders of magnitude lower than results reported recently for short MoSi devices with shunt resistors. We also found that 5 nm thick MoSi detectors with the same geometry were insensitive to single near-infrared photons, which may be associated with different levels of suppression of the superconducting order parameter. However, our results obtained on 3 nm thick MoSi devices are in a good agreement with predictions in the frame of a kinetic-equation approach.